The present invention relates to an ink composition.
A color image is formed on a recording medium using color inks (e.g., cyan ink, magenta ink, yellow ink, and black ink). In recent years, an ink that can form an image having a color that cannot be obtained using only the color inks has attracted attention. For example, a white ink composition that includes a white coloring material such as titanium dioxide has attracted attention. The white ink composition can form a white image that cannot be obtained using the color inks.
For example, when recording a color image on a recording medium that may have a color other than white (e.g., plastic product or metal product), the white ink composition may be used to cancel out the color of the recording medium in order to improve the color development capability of the color image. When recording a color image on a transparent sheet, the white ink composition may be used to form a white shield layer that reduces the transparency of the color image. Therefore, the white ink composition is required to exhibit an improved white color development capability when the white ink composition is caused to adhere to the recording medium.
The white color development capability when the white ink composition is caused to adhere to the recording medium has been improved by increasing the concentration of the white coloring material included in the white ink composition, or increasing the particle size of the white coloring material. However, the rub fastness of the white image formed using the white ink composition may be impaired when the concentration of the white coloring material is increased. On the other hand, when the particle size of the white coloring material is increased, the white coloring material may precipitate in the ink composition. Specifically, an improvement in white color development capability has a trade-off relationship with the occurrence of precipitation or deterioration in rub fastness. For example, JP-A-2007-211176, JP-A-2006-274214, and JP-A-2012-233148 disclose a method that utilizes porous titanium dioxide particles as the white coloring material in view of the above problem.
When porous titanium dioxide particles are used as the white coloring material, the occurrence of precipitation may be reduced. However, since the use of porous titanium dioxide particles cannot sufficiently improve the shield capability and the color development capability of the recorded white image, a further improvement in white color development capability has been desired.